1. Field of the invention:
The present invention relates to a wear testing device used for measuring the amount of wear of a sliding material, and more particularly, to a pin-on-disk type wear testing device in which a pin type testpiece is in contact with a rotating disk under a constant load for measuring the amount of wear of the pin type testpiece.
2. Description of the prior art:
As a wear testing device for measuring the amount of wear of a sliding material, a pin-on-disk type wear testing device is known in which a pin type testpiece to be measured for wear is stationarily in contact with a rotating disk type testpiece for measuring the rate of wear of the pin type testpiece with respect to time. With the pin-on-disk type wear testing device, the following two kinds of methods for measuring the wear rate have been used: Method "A" in which the rate of weight loss from the pin type testpiece which slides against the rotating disk type testpiece is measured with respect to time to calculate the rate of wear with respect to time; and Method "B", as shown in FIG. 3, a rotating disk type testpiece 13 is mounted on a disk type testpiece table 12 that is supported in a base 11 to which a contact or noncontact type displacement gauge 18 is fixed for detecting the progressive amount of displacement between the base 11 and a pin type testpiece 14 in contact with the disk type testpiece 13 under a constant load, and the amount of wear of the pin type testpiece 14 is measured by the amount of displacement.
In method "A", since the pin type testpiece must be dismounted from the wear testing device at specified intervals of time for measurement of its weight and then refitted to the wear testing device for continued testing, the test efficiency is greatly sacrificed. Moreover, when the pin type testpiece once dismounted is refitted to the wear testing device, the pin type testpiece cannot be positioned to contact the disk type testpiece at the same position where it had been in contact with the disk type testpiece before the removal therefrom, with a resultant change in the condition of the wear debris existing between the pin type testpiece and the disk type testpiece, hampering accurate measurement of the wear of the pin type testpiece with respect to time. Furthermore, at the time of the weight measurement, if the pin type test-piece absorbs moisture with a resultant change in its weight, it is not possible to accurately measure the amount of wear of the pin type testpiece.
On the other hand, method "B" allows continuous measurement of the wear rate of the pin type testpiece with respect to time. However, since the displacement gauge 18 is fixed to the base 11 of the wear testing device, the amount of displacement measured by the displacement gauge 18 represents the absolute displacement with respect to the base 11. This means that the amount of displacement measured by the displacement gauge 18 includes not only the wear loss .DELTA.h of the pin type testpiece but also the error .DELTA.h' caused by the displacement of the disk type testpiece with respect to the base 11. The cause of the error .DELTA.h' includes the displacement caused by an axial positional change of the disk type testpiece 13 due to its rotational motion, a circumferential waving motion of the disk type testpiece 13, and the thermal expansion of whole device due to thermal changes such as heat generation through the friction between the pin type testpiece and the disk type testpiece, all of which combine to prevent accurate measurement of the wear rate of the pin type testpiece 14 with respect to time.